The invention relates to an improved ink jet printhead and to a vent system for maintaining desirable environmental conditions within the printhead.
Ink jet printers typically include a print head having either heaters or piezoelectric devices for ejecting ink during printing. In either case, liquid ink is directed from a reservoir to a plurality of chambers, each associated with a heater or piezoelectric device and a nozzle. The heaters/piezoelectric devices are electronically controlled to eject ink in a desired sequence that corresponds to the image to be printed.
To provide desirable conditions for controlling the flow of ink from the reservoir to the chambers, the reservoir may initially be placed under a condition of a slight vacuum with respect to ambient pressure. The vacuum condition is commonly referred to as a xe2x80x9cbackpressurexe2x80x9d. In order to maintain a desired backpressure in the reservoir throughout the operating life of the printhead, a pressure regulating device may be included. The pressure regulating device is intended to help maintain a desired negative pressure in the reservoir and adjust against pressure changes in the reservoir resulting from, for example, increases or decreases in operating temperatures and pressures (e.g., hot, cold or altitude changes or pressure changes associated with air travel) and from pressure changes associated with a decrease of the volume of ink in the reservoir through use of the printhead.
One problem associated with pressure regulators is that the pressure regulators are often made from materials that are permeable to water vapor. Water evaporating from the ink tends to flow by diffusion to areas of lower relative humidity, in this case, the pressure regulator chamber. The relative humidity of the pressure regulator chamber is affected by air flow into the chamber from the atmosphere exterior to the ink reservoir as the volume of ink in the reservoir decreases. The flow of air affects the relative humidity of the chamber providing a relative humidity differential that induces water evaporation from the ink and net water vapor flow into the chamber.
Some printheads further include so-called xe2x80x9cbubble generators.xe2x80x9d Bubble generators generally include a valved orifice that permits controlled flow communication of air between the interior and the exterior of the ink reservoir. Such bubble generators are generally designed to permit air to xe2x80x9cbubblexe2x80x9d into the reservoir to increase the pressure within the reservoir (i.e., reduce the vacuum). A problem attendant to bubble generators is leakage of ink to the exterior of the reservoir. Another problem is drying of ink in the reservoir adjacent the bubble generator which leads to dysfunction, causing undesirable reservoir environmental conditions and reduction in printhead operation and longevity.
The present invention relates to a vent system for use with ink jet pens of the type having internal pressure regulators. The vent system advantageously functions to maintain desirable environmental conditions within the ink jet pen for improved pen operation and longevity. In addition, for pens of the type having an internal pressure regulator in flow communication with the bubble generator, the vent system functions to inhibit ink leakage from the pen.
With regard to the above and other objects and advantages, the invention provides a vent system for an ink jet pen of the type having an internal pressure regulator. The vent system provides air flow communication between the exterior of the ink jet pen and an interior chamber associated with the pressure regulator while substantially inhibiting the flow of water vapor from the chamber to the exterior of the pen.
In a preferred embodiment, the invention provides an ink jet pen having an exterior portion and an interior portion, and a pressure regulator within the interior portion including a chamber associated therewith. The vent system is provided by an elongate air flow path defined adjacent the exterior of the pen, the flow path having a first end in flow communication with the chamber of the internal pressure regulator and a second end in flow communication with the exterior of the pen. It is particularly preferred that the vent system be configured to substantially inhibit water vapor flow to the exterior of the pen from the chamber of the pressure regulator.
In another aspect the invention provides an ink cartridge for an ink jet printer. The cartridge includes a body portion including a first panel portion having an interior surface opposite an exterior surface, a second panel portion attachable to the body portion to define a cavity for containing ink between the first panel portion and the second panel portion, and a chamber defined within the cavity adjacent the interior surface of the body portion. A lung type pressure regulator is disposed within the cavity adjacent the chamber. An air diffusion path provides flow communication between the exterior surface of the body portion and the chamber. The air diffusion path includes an elongate flow path defined adjacent the exterior surface of the body portion, the flow path having a first end in flow communication with the chamber and a second end in flow communication with the exterior surface of the body portion, whereby flow of water vapor out of the chamber is significantly inhibited.
As described in more detail below, the vent system advantageously helps to maintain a desirable climate within chamber of the pressure regulator so that water evaporation from the ink is inhibited. In particular, the vent system is configured to maintain a relatively humid environment within the chamber associated with the pressure regulator while permitting air flow into and out of the chamber. By maintaining the humidity of the chamber above a desired value, water vapor permeation through the lung material from the ink is minimized. Hence the water content of the ink in the pen over time remains relatively constant. Loss of water from the ink is detrimental to the operation of the pen. In addition, when incorporated in ink jet pens of the type having a bubble generator in flow communication with the chamber of the pressure regulator, the vent system functions to reduce the incidence of ink leakage to the exterior of the pen.